The present invention relates to an axle support of a motor vehicle, having an at least approximately planar reinforcement element which is configured as a fiber-composite component and is fastened to individual supports of the axle support. With respect to the prior art, reference is made in particular to German patent publication no. DE 10 2008 006 006 A1; moreover, European patent no. EP 0 941 912 B1 should also be stated as a further example of a motor vehicle axle support (therein also referred to as “sub frame”) having a planer reinforcement element (therein also referred to as “shear area”).
In the event of a crash (accident, impact on or collision with an obstacle) high forces act on the axle supports in a motor vehicle, that is to say on the front-axle support and on the rear-axle support, said high forces being capable of leading to deformation and partial destruction of the respective axle support and thus also in places of the body connected thereto. In order for the crash safety of a motor vehicle to be improved, reinforcement elements, so-called shear areas, are thus connected, preferably (releasably) screwed to the axle supports, which have comparatively high rigidity and torsional rigidity and are capable of suitably distributing the impulse of an impact across the axle support and/or to thus dissipate the same in structures of the motor vehicle. Such conventional reinforcement elements are made from metallic materials, in particular from steel or aluminum. On account thereof, a high weight is added to the motor vehicle. In order for this to be avoided, a planar axle-support reinforcement element composed of or manufactured from a fiber-composite material, respectively, (or from a fiber-reinforced plastic, respectively) has already been proposed.
The intention is to propose herein how such a fiber-composite reinforcement element of a vehicle axle support may be further improved in terms of its mechanical properties, in particular for the event of a vehicle crash, this being the object of the present invention.
The achievement of this object is characterized in that the reinforcement element is constructed from multiple layers and apart from a lower and an upper cover layer has at least one intermediate layer which in an analogous manner to the cover layers extends at least approximately across the entire area, endless-fiber tapes having aligned and oriented fibers being incorporated thereabove and therebelow.
A reinforcement element according to the invention is designed in the form of an at least approximately planar fiber-composite component, and in the installed state of said reinforcement element on the vehicle axle support, between the upper side thereof (i.e. upper cover layer) facing the vehicle bodywork and the lower side thereof (i.e. lower cover layer) facing the roadway, oriented endless-fiber tapes are integrated in the fiber-composite material. It is provided here that a lower layer of fiber tapes, which is thus adjacent to the mentioned lower cover layer and is formed from a plurality of individual fiber tapes, and an upper layer of fiber tapes, which is thus adjacent to the mentioned upper cover layer and is formed from a plurality of individual fiber tapes, are mutually separated by a so-called intermediate layer which is practically congruent with the cover layers. While thus the two cover layers and the mentioned intermediate layer extend across a substantial region, or across a notably big area (parallel with the roadway) of the axle support, the interdisposed fiber tapes according to the invention are significantly narrower than the width measurement of the cover layer(s), measured in the transverse direction of the vehicle, or the length measurement of the cover layer(s), measured in the longitudinal direction of the vehicle. When likewise viewed in the transverse direction of the vehicle, the interdisposed fiber tapes extend at least from one of the main longitudinal chassis beams of the axle support to the other main longitudinal chassis beam of the axle support, the reinforcement element usually being fastened to those main longitudinal chassis beams.
As is known, a vehicle axle support is put together from a left-side and a right-side main longitudinal chassis beam which in each case extends at least approximately in the longitudinal direction of the vehicle, said main longitudinal chassis beams being interconnected by at least one, preferably a plurality of main transverse chassis beams which extend at least approximately in the transverse direction of the vehicle, said beams being also referred to here as individual supports of the axle support.
The aligned endless-fiber tape used above will now be explained. This is to be understood as a tape which is formed from said fibers, ultimately together with a plastic material, the fibers of said tape being aligned in a targeted manner, namely in the longitudinal direction of the tape. Fibers employed here include the generally so-called endless fibers. It has already been stated in the preceding paragraph that such a tape or endless-fiber tape, respectively, when viewed in its transverse direction, is notably narrower than the width measurement or length measurement of the reinforcement element. In an axle-support reinforcement element according to the invention, at least two such endless-fiber tapes are now provided between one of the cover layers which extends across the entire area over the reinforcement element and an intermediate layer which extends at least approximately in an analogous manner to said cover layers at least approximately across the entire area over the planar reinforcement element, said endless-fiber tapes being disposed such that when collectively viewed, they do not form a structure that extends across the entire area over the reinforcement element. Thus, for example, it is not a plurality of endless-fiber tapes that are disposed so as to be mutually parallel and directly adjacent to one another. Rather, these endless-fiber tapes are disposed such that they strengthen the reinforcement element in a targeted manner.
In terms of the arrangement and/or alignment of the endless-fiber tapes, the latter in an at least approximately rectangular reinforcement element (as is usual) may at least approximately extend along the two diagonals thereof and consequently intersect one another. Forces which are not introduced into the axle support in the longitudinal direction of the vehicle (for example due to a crash taking place in an oblique manner to the vehicle axis) are thus in particular absorbed in the best manner possible and dissipated. It is furthermore proposed that the endless-fiber tapes, when viewed in a vertical projection onto the reinforcement element which is fitted to the vehicle, is at least approximately congruent with at least one individual support of the axle support, or with the main longitudinal chassis beams thereof and/or one main transverse chassis beam. Particularly intensive reinforcement or force transmission, respectively, between the individual supports of the axle support and the planar fiber-composite material reinforcement element fastened thereto thus results.
Moreover, in one advantageous embodiment of the present invention the mentioned cover layers and/or the mentioned intermediate layer may also be designed with aligned fibers, that is to say fibers which are aligned or oriented in a targeted manner, respectively. With a view to favorable force transmission, both the lower as well as the upper cover layer may be formed on their part in each case from two layers of aligned fibers which in each case run in a mutually intersecting manner at an angle of approx. 45° in relation to the longitudinal axis of the vehicle, while the likewise preferably endless fibers of the intermediate layer run substantially in the transverse direction of the vehicle. Alternatively to the fiber orientation described this far in the cover layers and in the intermediate layer, random-laid mats having long fibers or short fibers which are not aligned in a targeted manner and which are preferably from recycled material may be employed for these layers.
As is generally the case in fiber-composite components, a fiber-composite reinforcement element according to the invention has a significantly reduced dead weight as compared to conventional metallic components. In order for good rigidity, strength and high torsional rigidity to be introduced into the component, according to the invention a plurality of endless-fiber tapes are integrated in the reinforcement element, each on its part being narrow in relation to the cover layers. On account of the use of aligned endless-fiber tapes according to the invention, stress paths which dissipate deformation forces or impact impulses acting thereon along the alignment of the endless-fiber tapes and thus are ultimately capable of distributing them in a targeted manner across the vehicle body are configured to be stable in a targeted manner in the reinforcement element, on account of which localized deformation and in particular destruction of vehicle structures can be effectively counteracted. The use of endless-fiber tapes furthermore has the advantage that the amount of material cutoffs during manufacturing of the fiber-composite shear area is reduced, since the endless-fiber tapes may be readily manufactured in the desired width and cut to length according to requirements. Tailored cutting of the contours of the tapes is not required. Cutting to length of the tapes may be readily and cost-effectively carried out by way of example by means of a guillotine blade or a punching operation, on account of which the manufacturing costs may be further reduced. Particularly preferably, the reinforcement element is designed as an SMC (sheet molding compound) or manufactured by plastic injection molding, as final machining of the fiber-composite component is also thereby dispensed with. The component having the desired geometry here is preferably configured in an off-tool manner, wherein the endless fibers terminate within the component and no tool run-out is required.
The fibers of the fiber-composite material may be carbon fibers and/or glass fibers and/or aramid fibers and/or basalt fibers, since these fiber materials are distinguished by ready availability and processability with very good stability and low dead weight. With a view to potential corrosion during interaction with surrounding metallic components, glass fibers are particularly advantageous.
In order for rigidity to be further increased, the at least approximately planar fiber-composite material reinforcement element of a vehicle axle support according to the invention may have at least one reinforcement structure in the form of one or a plurality of corrugations and/or of one or a plurality of thickness grades and/or of one or a plurality of ribs, meaning that the reinforcement element is structured in such a manner. Besides a corresponding and dedicated shaping of the cover layer or of the cover layers, incorporation into the reinforcement element of dedicated constructional elements, which may be preferably likewise formed from fibrous materials and may be configured, for example, by means of back-molding by injection-molding or by pressing in the SMC construction method and be connected to the planar fiber-composite reinforcement element, may also be considered. Adhesive connection of a dedicated strengthening element to the reinforcement element is likewise possible. In this way, best possible rigidity of the latter at the lowest possible weight is achievable. Preferably, such strengthening elements or strengthening structures which protrude from that plane of the approximately planar reinforcement element that is parallel with the roadway are provided on the upper cover layer which faces the vehicle bodywork, while the lower cover layer which faces the roadway is preferably configured so as to be smooth or planar, respectively, in order to achieve good aerodynamic properties. Damage due to stone chipping or similar may be prevented by providing a cover layer having glass fibers as fiber material.
Furthermore advantageously, corrosive stability of the reinforcement element and of the components which are adjacent thereto, such as in particular the individual supports of the axle support, but also wheel control arms or other components, is further increased in that a constructive air gap and/or a corrosion-inhibiting coating are/is provided at any connection points for attachment and fastening, that is to say at contact points between these components and the fiber-composite reinforcement element.
According to one advantageous refinement, a connection element and/or a receptacle provision or a connector device, respectively, for at least a further component may be integrated in the fiber-composite reinforcement element. Such a connection element or such a receptacle provision may be permitted to enable attachment or fastening of further components and/or fastening of the reinforcement element on the axle support or on parts of the vehicle bodywork and formed from a ceramic or metallic material, for example, or likewise from a plastic. By embedding or integrating such components in the fiber-composite component (reinforcement element), respectively, these mentioned components become a fixedly integrated component part of the fiber-composite component and enhance the functionality of the latter.
It is furthermore proposed that a visco-elastic material, preferably in the form of a tier of insulation material, which may be a rubber-elastic mat, for example, is provided in the shear area in order to achieve in particular acoustic damping properties of the shear area. This tier here may form a quasi-dedicated layer in the reinforcement element.
As a result of the design embodiments and refinements according to the invention, the following advantages result in particular: The mechanical properties of the reinforcement element, such as static and dynamic rigidity, are improved. The strength of the reinforcement element is increased. Crash behavior of the reinforcement element is improved by the fiber-composite construction technique being optimized in terms of material. Locally acting deformation energy may thus be decentralized and directed away in a targeted manner by way of the stress paths formed. Driving dynamics of the vehicle and the aerodynamic characteristics thereof and the acoustics may be improved by the reinforcement element according to the invention. The weight of the reinforcement element is lower than in conventional metal construction techniques, while offering the same or better functional properties. Integration and fastening of further components is enabled. Damage due to stone chipping may be easily prevented. The manufacturing process of the reinforcement element is simplified, as a result of which manufacturing costs may be reduced.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.